Abstract Background Transcatheter arterial embolization (TAE) has long been used for hemostasis of traumatic or postoperative hemorrhage and embolization of tumors. Previous retrospective studies of TAE for painful bone metastases showed 60%–80% pain reduction with a median time to response of 1–2 days. Compared with radiotherapy and bisphosphonates, time to response appeared earlier than that of radiotherapy or bone-modifying agents. However, few prospective studies have examined TAE for this indication. Here, we describe the protocol for a confirmatory study designed to clarify the efficacy and safety profile of TAE. Methods This study will be a multicenter, single-arm confirmatory study (phase 2–3 design). Patients with painful bone metastases from any primary tumor are eligible for enrollment. TAE will be the main intervention. Following puncture of the femoral artery under local anesthesia and insertion of an angiographic sheath, angiography will confirm that the injected region includes tumor vasculature. Catheter position will be adjusted so that the embolization range does not include non-target tissues. Spherical embolic material will then be slowly injected into the artery to embolize it. The primary endpoint (efficacy) is the proportion of subjects with pain relief at 72 h after TAE and the secondary endpoint (safety) is the incidence of all NCI Common Terminology Criteria for Adverse Events version 5.0 Grade 4 adverse events and Grade ≥ 3 necrosis of the central nervous system. Discussion If the primary and secondary endpoints are met, TAE can be a treatment choice for painful bone metastases. Trial registry number is UMIN-CTR ID: UMIN000040794. Trial registration The study is ongoing, and patients are currently being enrolled. Enrollment started in March 2021. A total of 36 patients have participated as of Aug 2022. Protocol Version: Ver1.4, 13/07/2022.
